Home > Community > Forums > RF Design > Layout help

Email

* Required Fields

Recipients email * (separate multiple addresses with commas)

Your name *

Your email *

Message *

Contact Us

* Required Fields
First Name *

Last Name *

Email *

Company / Institution *

Comments: *

 Layout help 

Last post Wed, Sep 15 2010 4:27 AM by Andrew Beckett. 5 replies.
Started by Mohana 07 Sep 2010 10:04 AM. Topic has 5 replies and 2781 views
Page 1 of 1 (6 items)
Sort Posts:
  • Tue, Sep 7 2010 10:04 AM

    • Mohana
    • Not Ranked
    • Joined on Tue, Apr 6 2010
    • Posts 12
    • Points 195
    Layout help Reply
     Hi,

    I am working on LC-VCO. the testbench for the schematic works fine but when i try the testbench for my layout it gives me error with the initial condition. The config mode works for c-only extraction. but when consider the complete paracitics, the transient analysis is stopped because of the error with the initial condition. i have attached a copy of my spectre.out file so reference.

    Please help me with this problem.


    Notice from spectre during topology check.
        No DC path from node `I7.avS22' to ground, Gmin installed to provide path.


    Circuit inventory:
                  nodes 237
                bsim3v3 20   
              capacitor 231  
                  diode 4    
               inductor 61   
        mutual_inductor 416  
               resistor 232  
                vsource 2    

    Time for parsing: CPU = 92.985 ms, elapsed = 135.311 ms.
    Time accumulated: CPU = 92.985 ms, elapsed = 135.311 ms.
    Peak resident memory used = 26.3 Mbytes.

    Entering remote command mode using MPSC service (spectre, ipi, v0.0, spectre1_12141_1, ).

    ***********************************************
    Transient Analysis `tran': time = (0 s -> 1 us)
    ***********************************************

    Warning from spectre during IC analysis, during transient analysis `tran'.
        WARNING (SPECTRE-16255): Initial condition of 1 mV between nodes voutn and 0 converted into initial guess (nodeset) because there is no capacitive path to ground.
    Warning from spectre during IC analysis, during transient analysis `tran'.
        WARNING (CMI-2743): I7.C0.d1: Junction current density(I/Area) exceeds `imelt'.  The results computed by Virtuoso(R) Spectre(R) are now incorrect because the junction current model has been linearized.
        WARNING (CMI-2743): I7.C1.d1: Junction current density(I/Area) exceeds `imelt'.  The results computed by Virtuoso(R) Spectre(R) are now incorrect because the junction current model has been linearized.

    Important parameter values:
        start = 0 s
        outputstart = 0 s
        stop = 1 us
        step = 1 ns
        maxstep = 20 ns
        ic = all
        skipdc = no
        reltol = 1e-03
        abstol(V) = 1 uV
        abstol(I) = 1 pA
        temp = 27 C
        tnom = 27 C
        tempeffects = all
        errpreset = moderate
        method = traponly
        lteratio = 3.5
        relref = sigglobal
        cmin = 0 F
        gmin = 1 pS


    Warning from spectre at time = 1 ns during transient analysis `tran'.
        WARNING (CMI-2743): I7.C0.d1: Junction current density(I/Area) exceeds `imelt'.  The results computed by Virtuoso(R) Spectre(R) are now incorrect because the junction current model has been linearized.
        WARNING (CMI-2743): I7.C1.d1: Junction current density(I/Area) exceeds `imelt'.  The results computed by Virtuoso(R) Spectre(R) are now incorrect because the junction current model has been linearized.

        tran: time = 31 ns        (3.1 %), step = 16 ns         (1.6 %)
        tran: time = 91 ns        (9.1 %), step = 20 ns           (2 %)
        tran: time = 131 ns      (13.1 %), step = 20 ns           (2 %)
        tran: time = 191 ns      (19.1 %), step = 20 ns           (2 %)
        tran: time = 231 ns      (23.1 %), step = 20 ns           (2 %)
        tran: time = 291 ns      (29.1 %), step = 20 ns           (2 %)
        tran: time = 331 ns      (33.1 %), step = 20 ns           (2 %)
        tran: time = 391 ns      (39.1 %), step = 20 ns           (2 %)
        tran: time = 431 ns      (43.1 %), step = 20 ns           (2 %)
        tran: time = 491 ns      (49.1 %), step = 20 ns           (2 %)
        tran: time = 531 ns      (53.1 %), step = 20 ns           (2 %)
        tran: time = 591 ns      (59.1 %), step = 20 ns           (2 %)
        tran: time = 631 ns      (63.1 %), step = 20 ns           (2 %)
        tran: time = 691 ns      (69.1 %), step = 20 ns           (2 %)
        tran: time = 731 ns      (73.1 %), step = 20 ns           (2 %)
        tran: time = 791 ns      (79.1 %), step = 20 ns           (2 %)
        tran: time = 831 ns      (83.1 %), step = 20 ns           (2 %)
        tran: time = 891 ns      (89.1 %), step = 20 ns           (2 %)
        tran: time = 931 ns      (93.1 %), step = 20 ns           (2 %)
        tran: time = 985.5 ns    (98.6 %), step = 14.5 ns      (1.45 %)
    Number of accepted tran steps =             54
    Initial condition solution time: CPU = 1.999 ms, elapsed = 2.04682 ms.
    Intrinsic tran analysis time:    CPU = 20.997 ms, elapsed = 20.75 ms.
    Total time required for tran analysis `tran': CPU = 24.996 ms, elapsed = 29.9191 ms.
    Time accumulated: CPU = 119.981 ms, elapsed = 1.02863 s.
    Peak resident memory used = 31.3 Mbytes.

    finalTimeOP: writing operating point information to rawfile.
    modelParameter: writing model parameter values to rawfile.
    element: writing instance parameter values to rawfile.
    outputParameter: writing output parameter values to rawfile.
    designParamVals: writing netlist parameters to rawfile.
    primitives: writing primitives to rawfile.
    subckts: writing subcircuits to rawfile.

     

     

    Thanks

    Asha
    • Post Points: 20
  • Wed, Sep 8 2010 12:07 AM

    Re: Layout help Reply

    You can't put initial conditions on a node unless there's a capacitive path to ground, as the message says. However, you said that the transient stops because of this error. First it's a warning, and second the transient continues - so I don't quite understand what your problem is...

    Regards,

    Andrew.

    • Post Points: 20
  • Wed, Sep 8 2010 9:31 AM

    • Mohana
    • Not Ranked
    • Joined on Tue, Apr 6 2010
    • Posts 12
    • Points 195
    Re: Layout help Reply

     Hi Andrew,

     The transient analysis is not right. if the analysis was working right then the percentage of progress wouldnot be 2%, it would vary.

     can you please explain more about the capacitive path to ground?


    Asha

    • Post Points: 20
  • Fri, Sep 10 2010 3:03 AM

    Re: Layout help Reply

    See http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNumber=11641178

    In Simulation->Options->Analog set "iccapcheck" to "no". Or add this:

    myoptions options iccapcheck=no

    To your netlist.

    Regards,

    Andrew.

     

    • Post Points: 20
  • Tue, Sep 14 2010 11:13 AM

    • Mohana
    • Not Ranked
    • Joined on Tue, Apr 6 2010
    • Posts 12
    • Points 195
    Re: Layout help Reply

     Hey Andrew,

    I tried the option mentioned by you but it didnt work.

    and also i am unable to view the link that u sent me. Is there any other way that i can access that link?

     

    Thank you

    Mohana 

    • Post Points: 20
  • Wed, Sep 15 2010 4:27 AM

    Re: Layout help Reply

    Mohana,

    I just checked it with an example that I used, and it allowed me to set an ic on a purely resistive node, and it worked. That said, I'm a bit suspicious if the node you are setting doesn't have a capacitive path to ground, I'd be surprised if it was really going to have an influence on the initial conditions of the oscillator.

    To access Cadence Online Support you need to register. 

    You  may have to contact customer support - either directly, or via your support channel if you're at a University - with details on what isn't working and with a testcase that shows the problem. Perhaps there's something wrong with the parasitic extraction?

    Or you need to apply your initial conditions to a different node - hard to tell without seeing the data.

    Regards,

    Andrew.

    • Post Points: 5
Page 1 of 1 (6 items)
Sort Posts:
Started by Mohana at 07 Sep 2010 10:04 AM. Topic has 5 replies.